Pleated construction for effecting gas transfer membrane

ABSTRACT

A contactor for effecting passage through a membrane from a first fluid a second fluid is provided. A cylindrical pleated membrane cartridge is positioned within a housing having a first inlet and a first outlet from a first fluid and at lest a second outlet for a second fluid. At least one baffle is positioned within a first flow path for the first fluid.

BACKGROUND OF THE INVENTION

This invention relates to a contactor and process to effect gas flowbetween two fluids including a pleated porous membrane. More particular,this invention relates to such a contactor including a pleated porousmembrane and a baffle means for effecting contact of a liquid streamwith the pleated membrane.

Microporous membranes are used in a wide variety of applications. Usedas separating filters, they remove particles and bacteria from diversesolutions such as buffers and therapeutic containing solutions in thepharmaceutical industry, ultrapure aqueous and organic solvent solutionsin microelectronics wafer making processes, and for pre-treatment ofwater purification processes. In addition, they are used in medicaldiagnostic devices, where their high porosity results in advantageousabsorption and wicking properties.

Hollow fiber membranes are used as membrane contactors, typically fordegassing or gas absorption applications. Contactors bring together twophases, i.e., two liquid phases, or a liquid and a gas phase for thepurpose of transferring a component from one phase to the other. Acommon process is gas-liquid mass transfer, such as gas absorption, inwhich a gas or a component of a gas stream is absorbed in a liquid.Liquid degassing is another example, in which a liquid containingdissolved gas is contacted with an atmosphere, a vacuum or a separatephase to remove the dissolved gas. In an example of conventional gasabsorption, gas bubbles are dispersed in an absorbing liquid to increasethe gas/liquid surface area and increase the rate of transfer of thespecies to be absorbed from the gas phase. Conversely, droplets ofliquid can be sprayed or the liquid can be transported as a thin film incounter-current operation of spray towers, packed towers, etc.Similarly, droplets of an immiscible liquid can be dispersed in a secondliquid to enhance transfer. Packed columns and tray columns have adeficiency as the individual rates of the tlwo phases cannot beindependently varied over wide ranges without causing flooding,entrainment, etc. If however, the phases are separated by a membrane,the flow rates of each phase can be varied independently. Furthermore,all the area is available, even at relatively low flow rates. Due tothese advantages, hollow fiber membranes are increasingly being used incontactor applications.

Hydrophobic microporous membranes are commonly used for contactorapplications with an aqueous solution that does not wet the membrane.The solution flows on one side of the membrane and a gas mixture at alower pressure than the solution flows on the other. Pressures on eachside of the membrane are maintained so that the liquid pressure does notovercome the critical pressure of the membrane, and so that the gas doesnot bubble into the liquid. Critical pressure, the pressure at which thesolution will intrude into the pores, depends directly on the materialused to make the membrane, inversely on the pore size of the membrane,and directly on the surface tension of the liquid in contact with thegas phase. Hollow fiber membranes are primarily used because of theability to obtain a very high packing density with such devices. Packingdensity relates to the amount of useful filtering surface per volume ofthe device. Also, they may be operated with the feed contacting theinside or the outside surface, depending on which is more advantageousin the particular application. Typical applications for contactingmembrane systems are to remove dissolved gases from liquids,“degassing”; or to add a gaseous substance to a liquid. For example,ozone is added to very pure water to provide a solution for washingsemiconductor wafers.

An advantage for contacting applications is that the very low surfacetension of hydrophilic membranes such as thermoplastic perfluorinatedpolymers allows use with low surface tension liquids. For example,highly corrosive developers used in the semiconductor manufacturingindustry may contain surface tension reducing additives, such assurfactants. These developers could not be degassed with typicalmicroporous membranes because the liquid would intrude the pores at thepressures used and permeate, causing solution loss and excessevaporation. In addition, liquid filling the pores would greatly add tothe mass transfer resistance of gas transport.

Microporous membranes have a continuous porous structure that extendsthroughout the membrane. Workers in the field consider the range of porewidths to be from approximately 0.05 micron to approximately 10.0microns. Such membranes can be in the form of sheets, tubes, or hollowfibers. Hollow fibers have the advantages of being able to beincorporated into separating devices at high packing densities. However,hollow fibers have the disadvantages that they are difficult to form andare therefore expensive.

Accordingly, it would be desirable to provide a contactor apparatuswhich effects gas transfer from one fluid phase to a second fluid phasewithout the use of hollow fibers. In addition, it would be desirable toprovide such a contactor which effects gas transfer between two fluidphases with improved gas transfer efficiency as compared with presentlyavailable contactors.

SUMMARY OF THE INVENTION

A contactor is provided comprising an outer housing, a pleated membranecartridge and one or a plurality of baffles positioned (a) between theinner surface of the housing and the outer surface of the pleatedmembrane cartridge or (b) within an inner diameter of the pleatedmembrane cartridge. The baffles effect fluid flow into the intersticesbetween the leaves of the pleated cartridge and in the direction of anoutlet for the fluid from the contactor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a broken side view of a contactor of this invention havingbaffles positioned on an outside surface of a pleated membranecartridge.

FIG. 2 is a broken side view of a contactor of this invention havingbaffles positioned on an inside surface of a pleated membrane cartridge.

FIG. 3 is a partial top view of a pleated cartridge used in the presentinvention.

FIG. 4 is a partial side view of a contactor of this inventionillustrating flow of one fluid.

FIG. 5 is a top view of a segmented baffle used in the presentinvention.

FIG. 6 is a partial top view of a baffle having teeth used in thepresent invention.

FIG. 7 is a top view of a baffle positioned on an inner surface of amembrane cartridge.

FIG. 8 is a cross sectional view of an alternative contactor of thisinvention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

In accordance with this invention, a contactor for two fluids isprovided wherein gas transfer is effected between the fluids. A firstfluid comprising a liquid stream is contacted with an inside surface oran outside surface of a pleated membrane cartridge while a second fluidis contacted with the remaining inside or outside surface of the filtercartridge. One cartridge surface in contact with the first fluid isprovided with one or a plurality of baffles which direct fluid flow intothe interstices between adjacent leaves of the pleated filter. Fluidflow is maintained within these interstices by a baffle positioned toprovide blockage in either (a) the space between the inner surface of ahousing for the cartridge and the outer surface of the cartridge or (b)the space inside the inner surface of the cartridge.

One or a plurality of baffles can be utilized along the height of thecartridge. The baffles can be formed of a single piece or from matingsegments such as two mating segments. The surface of the baffles can besmooth or one of the baffle surfaces can be provided with teeth thatextend into the interstices between the plates or leaves of thecartridge. The inclusion of the teeth provide more intimate contactbetween the membrane of the cartridge and the first fluid from which gasis removed or into which gas is provided.

The pleated membrane is formed of a membrane layer and a porous supportscreen layer as is well known in the art. Suitable hydrophobic membranesinclude those formed ofpolytetrafluoroethylene-co-perfluoromethylvinylether, (MFA),polytetrafluoroethylene-co-perfluoropropylvinylether, (PFA),polytetrafluoroethylene-co-hexafluoropropylene, (FEP), andpolyvinylidene fluoride, (PVDF). Both PFA Teflon® and FEP Teflon®thermoplastics are manufactured by DUPont, Wilmington, Del. Neoflon® PFAis a polymer available from Daikin Industries. MFA Haflon® is a polymeravailable from Ausimont USA, Inc., Thorofare, NJ. Preformed MFA Haflon®and FEP Teflon® tubes are available from Zeus Industrial Products, Inc.,Orangebury S.C. Other thermoplastics or their blends which are useful inthe practice of this invention include but are not limited topoly(chlorotrifluoroethylene vinylidene fluoride), polyvinylchloride,polyolefins such a polypropylene, polyethylene, polymethylpentene, ultrahigh molecularweight polyethylene, ultrahigh molecular weightpolyethelene (UPE), polyamides, polysuflones, polyetheretherketones, andpolycarbonates.

Referring to FIG. 1, one embodiment of a contactor of this invention 10is shown. The contactor 10 includes a housing 12 having bonded end caps14 and 16. End cap 14 includes a liquid inlet 18. End cap 16 includes aliquid outlet 20 and an outlet 22 converted to a vacuum source (notshown). A pleated membrane cartridge 24 surrounded by a porous supportcage 26 is provided to support the cartridge 24. A second porous supportcage also can be positioned within the central core 28 of the cartridge24. Baffles 30 extend around the outer circumference of the cartridge24. The baffles 30 extend from the outer surface 34 of the cage 33 tothe inner surface of the housing 12. The baffles 30 function to directliquid into the interstices 38 between plate 40 thereby to provide moreintimate contact between the pleated membrane of the pleats 40. In thisembodiment, gas bubbles are removed from liquid introduced through inlet18.

In a second embodiment, a pressurized gas such as ozone can beintroduced through opening 22 under conditions to effect transfer ofozone through the pleated membranes into the liquid such as waterintroduced through inlet 18. If desired a second outlet from the housing(not shown) for the pressurized gas can be provided to remove thepressurized gas from the housing 12.

Referring to FIG. 2, a contactor 42 is provided wherein baffles 44 arepositioned within the core 46 of the pleated filter cartridge 48. Thecartridge 48 is surrounded by porous support cage 50. Liquid to bedegassed is introduced through inlets 52 and 54 into the central core 46of the cartridge 48. The baffle 44 causes the introduced liquid to moveinto the interstice between the pleats 60 to effect more intimatecontact with the membrane in the pleats 60. A vacuum source (not shown)is connected to outlet 62 to collect gas passing through the pleats 48.Degassed liquid is recovered through outlet 64.

In another embodiment, pressurized gas can be introduced into housing 66through outlet 62 under conditions to effect gas flow, such as ozoneinto liquid introduced through inlets 52 and 54.

Referring to FIG. 3, the pleats 24 of the cartridge 10 of FIG. 1, arepositioned between porous cage 36 and porous cage 41. Cage 36 contactsbaffle 30 positioned within housing 12.

Referring to FIG. 4, the baffles 30 cause the liquid to move into thepleats 40 as shown by arrow 65 and 67 to effect more intimate contactbetween the liquid and the membrane.

Referring to FIG. 5, the baffle 70 is formed from two baffle segments 71and 72 which contact each other during use.

Referring to FIG. 6, the baffle 73 includes teeth 75 which fit intointerstices between adjacent pleats of the cartridge 24 thereby toeffect more intimate contact between the liquid and the membrane. Whenthe baffle is positioned within the core of the cartridge as shown inFIG. 3, the teeth are on the outside surfaces of baffles 44.

As shown in FIG. 7, the baffle 44 of FIG. 2 comprises a solid piece.

Referring to FIG. 8, one embodiment of a contactor of the invention 10is shown. The contactor 10 includes a housing 12 having bonded end caps14 and 16. End cap 14 includes a liquid inlet 18. End cap 16 includes aliquid outlet 20 and an outlet 22 converted to a vacuum source (notshown). A pleated membrane cartridge 24 surrounded by a porous supportcage 26 is provided to support the cartridge 24. A second porous supportcage also can be positioned within the central core 28 of the cartridge24. Baffles 30 a extend around the outer circumference of the cartridge24. The baffles 30 a extend from the outer surface 34 of the cage 33 tothe inner surface of the housing 12. The baffles 30 a function to directliquid into the interstices 38 between plate 40 thereby to provide moreintimate contact between the pleated membrane of the pleats 40. In thisembodiment, gas bubbles are removed from liquid introduced through inlet18.

In a second embodiment, a pressurized gas such as ozone can beintroduced through opening 22 under conditions to effect transfer ofozone through the pleated membranes into the liquid such as waterintroduced through inlet 18. If desired a second outlet from the housing(not shown) for the pressurized gas can be provided to remove thepressurized gas from the housing 12.

The following example illustrates the present invention and is notintended to limit the same.

EXAMPLE 1

The apparatus of FIG. 1 having a 0.05 micron hydrophobic ultrahighmolecular weight polyethylene membrane (3500 cm² area) was tested withdeionized water to remove gas from the water. There were no visual signsof any bubble

being present at the outlet of the apparatus. The efficiency ofdegassing, as measured with a YSI 5100 Dissolved Oxygen Meter was 21%and 10% removal at a flow rate of 0.5 liter/min. and 2.0 liter/1 min.respectfully. These results compare with 8.0% with a PFA hollow fibermembrane contactor at a flow rate of 2.0 liter/1 min.

1. A contactor apparatus for effecting passage of gas through a membranefrom a first fluid to a second fluid which comprises: a cylindricalpleated membrane cartridge positioned within a housing, said housinghaving a first inlet and a first outlet for a first fluid and at least asecond outlet for a second fluid, and at least one baffle positionedwithin a first flow path for said first fluid.
 2. The apparatus of claim1 having a plurality of baffles.
 3. The apparatus of claim 1 whereinsaid at least one baffle is positioned on an outside surface of saidcartridge.
 4. The apparatus of claim 1 wherein said plurality of bafflesare is positioned on an outside surface of said cartridge.
 5. Theapparatus of claim 2 wherein said at least one baffle is positioned onan outside surface of said cartridge.
 6. The apparatus of claim 2wherein said plurality of baffles are is positioned on an outsidesurface of said cartridge.
 7. The process for removing gas from a firstfluid which comprises introducing said first fluid into said first inletof the apparatus of claim 1 and removing said first fluid from saidfirst outlet and applying a vacuum to said second inlet.
 8. The processof claim 7 wherein said second inlet is in fluid communication with acore of said cartridge and said baffles are positioned on an outsidesurface of said cartridge.
 9. The process of claim 7 wherein said secondinlet is in fluid communication with a an outside surface of saidcartridge and said baffles are positioned on an inside surface of saidcartridge.
 10. The process for removing gas from a first fluid whichcomprises introducing said first fluid into said first inlet of theapparatus of claim 1, introducing said first fluid from said firstoutlet and introducing a pressurized gas into to said second inlet. 11.The process of claim 10 wherein said second inlet is in fluidcommunication with a core of said cartridge and said baffles arepositioned on an outside surface of said cartridge.
 12. The process ofclaim 10 wherein said second inlet is in fluid communication with anoutside surface of said cartridge and said baffles are positioned on aninside surface of said cartridge.
 13. The process of claim 10 whereinsaid pressurized gas is ozone.
 14. The process of claim 11 wherein saidpressurized gas is ozone.
 15. The process of claim 12 wherein saidpressurized gas is ozone.
 16. The apparatus of any one of claims 1, 2,3, 4, 5 or 6 wherein at least one of said baffles includes teethpositioned to extend into interstices between pleats of said cartridge.